Ulster upset by final score (6)
I believe the answer is:
result
'final score' is the definition.
(I've seen this before)
'ulster upset' is the wordplay.
'upset' is an anagram indicator.
'ulster' is an anagram of 'RESULT'.
'by' acts as a link.
(Other definitions for result that I've seen before include "Consequence or effect" , "'Outcome, consequence (6)'" , "Ulster (anag) - outcome" , "Rustle (anag.)" , "Effect - outcome" .)